The solid electrolytic capacitor is known to be manufactured by forming a dielectric oxide film on a metal surface through anodic oxidation and bringing this film into contact with a solid electrolyte. The solid electrolytic capacitor for which a conductive polymer is used as the solid electrolyte has been proposed.
As examples of the metal covered with a dielectric oxide film through anodic oxidation, aluminum, tantalum, niobium, etc. are known.
As conductive polymers used for a solid electrolytic capacitor, conjugated conductive polymers such as polythiophene, polypyrrole, polyaniline, polyacetylene, polyphenylene, poly(p-phenylenevinylene), polyacene, polythiophenevinylene, and derivatives thereof are known. The technology to dope these conjugated conductive polymers with a poly anion such as polystyrene sulfonate as a counter anion is known.
Generally, a solid electrolyte is formed by chemically oxidizing and polymerizing or electropolymerizing a monomer solution for obtaining a conductive polymer and an oxidant solution on the dielectric oxide film formed on the surface of metal exhibiting valve action. In addition, another method of forming a solid electrolyte by applying a conductive polymer solution or suspension liquid to a metal surface has been proposed.
For example, Patent Document 1 discloses the manufacturing method including the steps of; forming a first solid electrolyte layer by impregnating a capacitor element with a conductive polymer dispersion solution in which conductive polymer particles are dispersed; and forming a second solid electrolyte layer by impregnating the surface of this first solid electrolyte layer with a solution containing a heterocyclic monomer and then a solution containing an oxidant or with a mixed solution containing a heterocyclic monomer and an oxidant.
Furthermore, Patent Document 2 discloses the manufacturing method including the steps of: forming a conductive polymer layer as a solid electrolyte layer on a capacitor element in which a dielectric oxide film is formed on the surface of a sintered body formed by sintering valve metal powders, by chemically polymerizing a polymerizable monomer; immersing this capacitor element in a conductive polymer solution or applying a conductive polymer solution to this capacitor element; drying this capacitor element; and forming another conductive polymer layer on the conductive polymer layer formed by the chemical polymerization.
Still furthermore, Patent Document 3 proposes the process to prepare a poly(3,4-ethylenedioxythiophene)-polystyrenesulfonate (commonly known as PEDOT-PSS) dispersion liquid with a lower viscosity to impregnate a capacitor with a conductive polymer by polymerization under ultrasonic irradiation.